Bicycle helmet laws could do more harm than good

Helmet laws like those in effect in Australia levy a substantial cost on healthcare systems because savings from fewer head injuries pale in comparison to the costs incurred by decreases in cycling, a mathematical model concludes.

Piet de Jong, a mathematician at Macquarie University in Sydney, Australia, estimates that bicycle helmet laws would cost the US $4.8 billion per year, Netherlands $1.9 billion, and the U.K $0.4 billion.

However, one critic contends that de Jong's methods overestimate the health benefits of cycling, as well as the drop in cyclists caused by helmet laws.

"There's a lot of uncertainty around it," de Jong admits. "I try to reconcile all these various numbers or proportions that impinge on the question of whether helmet laws are very useful."

He concludes that only under extreme, theoretical circumstances do mandatory helmet laws not end up costing the healthcare system. Head injuries must be a substantial proportion of bicycling injuries, few riders must abandon their bikes due to helmet laws, and the health benefits of cycling need to be low.

"Even under very favourable assumptions to the pro-helmet lobby group, it's very hard to get a benefit," de Jong says.

Numbers debate

Precise numbers on the costs and benefits of cycling and the use of helmets are hard to come by and often contentious.

Writing in the BMJ in 2006, Dorothy Robinson, a statistician at the Department of Primary Industries in Armidale, Australia, claimed that helmet laws caused bike ridership decreases of 20 to 40 per cent in several Australian cities and states.

"What she has never shown to my satisfaction, or that of other critics of her work, is how long the decline persisted," says Barry Pless, an epidemiologist at Montreal Children's Hospital in Canada.

In an attempt to circumvent all of this uncertainty, de Jong created a model that can be adjusted by putting in various values for drops in cycling rates due to helmet laws, the cost of an accident due to not wearing a helmet, and the overall health benefit of cycling.

"Everybody takes one piece of the evidence and nobody is really putting in all the pieces of the puzzle," he says.

Heart benefits

Under most parameters, de Jong's model concluded helmet laws would come with a net health cost. Exactly what cost is hard to determine. To come up with a figure of $4.8 billion for the US, he assumed the health benefit of cycling was a generous $1 per kilometre. However, as long as the benefit of cycling is not zero, there will be a net cost incurred due to helmet laws, he says.

Pless, though, contends that de Jong's model overvalues the health benefits of recreational cycling. Most riders travel short distances rather slowly, blunting some of cycling's cardiovascular benefits. He points to a study of 9000 UK government employees which found that people between the ages of 45 and 64 needed to pedal 40 kilometres per week to see any reduction in heart disease rates.

Despite these issues, de Jong hopes policy makers will take a good look at his paper before supporting legislation mandating helmet use.

However de Jong, a native of bike-loving Holland, makes clear that he would not discourage people from wearing helmets. "I go to Holland and places like that, and I don't wear a helmet," he says. "I used to live in London, and I wore a helmet all the time."

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